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RAID 5 for C sounds like a waste of money. If it's for TempDB, then move that to it's separate RAID 10 partition if you can. Other than that, RAID 10, while more expensive, does offer better performance for relational systems with heavy WRITEs. Whether your case meets that is not something we could assess, but you can measure that.
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SchmitzITMay 10 '13 at 21:15

It's impossible to give a focused answer to this question without more information. What is your read/write ratio? What is the typical workload? How good is your SAN's caching mechanism, and how much cache is there? Is this data mission-critical or is it archive data? And on and on...
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Jon SeigelMay 11 '13 at 12:34

3 Answers
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I did a series of TCP-C tests against several of the common RAID levels and was surprised that in a write-heavy scenario RAID5 was over 3x slower than RAID10 (it was 319% slower, to be specific). Your mileage may vary according to the actual ratio of reads versus writes in your scenarios.

+1 but... surprise? Granted the 3x over R10 you recorded is worse than expected but the scale of RAID write penalties tends to hold true across "typical" workloads.
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Mark Storey-SmithMay 11 '13 at 0:25

I would prefer RAID 10, by at least an order of magnitude, if you can afford it. The write performance is really tough to match, and while the read performance is slightly lower, this is only a factor in cases where your memory is completely inadequate (since typically most reads should not be physical).

While a bit dated, here is a great set of data from Kendal Van Dyke to back that up (these links are the intro and the summary; the former has links into all of the parts):

I am not sure you are setting up a SQL on VM or Physical. If it is VM, storage decision may vary as it is depends on the VM Host.

I recommend not to install SQL on C drive, dedicate the SQL for OS and OS only. So, it can be small but make sure to mirror the C drive, because if C drive give up whole sever needs to rebuilt.

As everyone suggest, RAID 10 much better than RAID 5 when it comes to IO. At the same time, RAID 5 works great on Indexing because it reads faster than RAID 10. RAID 10 good for LOG and TEMP DB. Many cases DATA and INDEX as well. We use RAID 10 most of the time.